A light-emitting diode (LED) could be detached from an inside PC board and extended to be installed on the housing of an electronic machine for showing the lighting state of the LED. However, such an activity is too tedious and lack of stability for a person to perform. Instead, a widely adopted approach is to move the LED together with a PC board as closer as possible to a predetermined through hole in the machine housing for showing its lighting state clearly through a light-pervious block. This approach is established on the premise of a shortest clearance between the LED and the light-pervious block. It results in difficult conditions in the arrangement of the PC board and the light source and the available space between them. Moreover, cross interference of neighboring light-pervious blocks might be incurred to confuse people with the lighting state of the light-pervious blocks that needs to be distinctly isolated.